1. Field of Invention
This invention relates to collecting broadcast audience listenership data by identifying the source of a broadcast signal through means of intercepting the audio portion coincidentally with a mobile telephone call and comparing the intercepted audio with a plurality of possible directly received broadcast signals.
2. Description of Prior Art
Broadcast ratings are traditionally estimated by submitting diaries to survey panelists with the request to record their radio or television (TV) listening habits. This method of statistical information gathering has limited accuracy because it relies on each sampled panelist's memory, diligence, and commitment. It also cannot provide quick or even near-instantaneous audience survey results that could be used to gauge audience interest and alter program content accordingly.
There has been considerable recent interest in the development of automatic systems and methods for measuring radio broadcast audience listenership. For example, U.S. Pat. No. 4,718,106, to Weinblatt, describes a technique that employs a survey signal added to or injected into the broadcast audio signal, which is picked up by a microphone in a portable signal detector, worn by an audience survey panelist. Any broadcast sound signals within listening range are picked up by the detector and tested to see if an injected survey signal is recognized. If one is detected, the appropriate information is time-stamped and stored in the detector memory, to be read out and reported a later time. A number of more recent disclosures, for instance U.S. Pat. Nos. 5,574,962, 5,581,800, 5,787,334, all to Fardeau, et al., U.S. Pat. No. 6,035,177, to Moses and Lu, and U.S. Pat. No. 6,151,578, to Bourcet, et al., expand this concept by encoding and embedding the survey signal(s) in such a way that they are inaudible to the listener. As with Weinblatt, these call for decoding devices installed permanently, or carried by survey panelists, nearby the actual sound signal, and for subsequent, delayed readout of data stored in decoding device memory. For an adequate survey, especially for measuring listenership of smaller radio stations, a large number of such devices must be deployed. A requirement for later readout precludes gathering timely listenership information. In order to avoid such delays, an extensive communications network must be dedicated or expensive use of existing networks, such as those for cellular calling, must be employed. U.S. Pat. No. 4,584,602, to Nakagama, describes such a TV survey system that uses injected marker signals and (near-) real-time use of the fixed telephone infrastructure.
U.S. Pat. No. 4,955,070, to Welsh and Foudraine, describes an alternative approach free of an injected survey signal. This approach also employs a portable monitor using a microphone to pick up broadcast audio sounds (an alternative calls for the use of an electromagnetic sensor to pick up emanations from currents driving a transducer, such as an earphone). However, a tuner within the monitor independently selects broadcasts of interest and a built-in processor tests the tuner output against the sounds picked up by the microphone or electromagnetic sensor in order to determine if a match occurs. Again, if a match is detected, the information is stored for later readout (at night), using a base unit. Welsh and Foudraine describe the preferred match process as “autocorrelating” the signals, but an autocorrelation process is actually incapable mathematically of producing a match. The Welsh and Foudraine approach also suffers from the difficulties of providing timely information and of requiring a large number of complex and expensive monitors for an accurate survey, just as with the systems described above.
U.S. Pat. No. 5,594,934, to Lu and Cook, disclose an audience survey “correlation meter” whereby in one embodiment portable monitoring devices with microphones pick up broadcast sound signals and compare them sequentially with “snippets” taken from broadcast signals of interest. The snippets, or “reference side representations” derived from them, are transmitted sequentially to the portable monitoring devices, where they are correlated with the broadcast sound signals. Matches found by the correlation process are stored for later recovery. This approach also suffers from the difficulties of providing timely information and of requiring a large number of complex and expensive monitors for an accurate survey. An alternative embodiment described by Lu and Cook shifts the correlation process from the portable monitors to a fixed location within a structure where survey data are desired. Pick-ups such as microphones, photodetectors, or induction coils are associated with nearby radio or TV receivers whose outputs are to be monitored. Simultaneously, a bank of individually tuned receivers comprising part of the fixed location correlation meter receives a plurality of carriers that have been mixed with a corresponding plurality of picked-up receiver outputs. Also simultaneously, the fixed correlation meter receives, via an antenna link, reference side representations (snippets) from an external source, and performs a zero-crossing correlation operation with a plurality of signals derived by stripping off the carriers. Any matches declared are downloaded to a remote point, perhaps via public telephone lines. This system relies on simultaneous and continuous transmission of numerous electromagnetic signals and is thus useable only for short-range, local installations. Both of the Lu and Cook embodiments require the broadcast of snippet information over a large area, with multiple correlation meters, in order to provide a statistically accurate survey, which requires a powerful transmitter of its own.
In U.S. Pat. No. 5,410,724, to Worthy, discloses a remote vehicular radio audience survey system that depends on detection of the local oscillator (LO) signal. LO signals are inadvertently radiated as part of the standard receiving process and are unique to each broadcast station tuned in. These radiations may be detected by roadside installations (remote survey sites) as vehicles pass by. In U.S. Pat. No. 5,749,043, also to Worthy, discloses a system primarily employing LO sensing at numerous remote survey sites, a central office, and sites to access data from the central office. Meanwhile, radio broadcasts are to be monitored in the central office, or elsewhere, to determine programming, by undisclosed means, possibly digitized and stored, or otherwise identified, so that they may be associated with LO survey results. Besides being rather unwieldy, and apparently requiring human intervention, most of these steps are unnecessary, as the LO signals, to the extent that vehicular radios follow the de-facto industry standard design, uniquely identify the broadcast source in an geographical area, because stations sharing the same frequencies are spaced far apart in order to minimize interference. A large number of survey sites need to be installed in order to adequately cover a geographical area. In U.S. Pat. No. 5,819,155, to Worthy and Dubrall, discloses a system to overcome limitations of LO sensing for the AM radio band. In this system, survey signals are to be injected on top of specified broadcast signals as vehicles pass by survey sites and, if a radio is tuned to a specified broadcast station, the resulting disturbance is sensed externally to the vehicle, specifically by sensing the weak magnetic effect produced by loudspeakers. This may produce objectionable interference to listeners and requires the expensive and intrusive installation of a large magnetic loop in the roadway.
U.S. Pat. No. 5,839,050, to Baehr and Chambers, describe a survey system wherein roadside survey sites attempt to sense the any inadvertent “intermediate frequency” (IF) emanations from vehicular radios. However, the signal described therein is actually an LO signal, and the process is similar to that described in U.S. Pat. No. 5,410,724, to Worthy, and therefore shares the same limitations. True IF emanations are even weaker that LO emanations and are therefore harder to detect. In addition, a match process such as cross-correlation with broadcast signals of interest would have to be provided in order to identify the broadcast source.